The present invention relates to electrical switches for selecting one of a plurality of functions, and to circuits which employ pressure responsive, variable impedance devices.
A wide variety of electrical equipment allow the user to select among several functions or operating modes. For example, the instrument panel of an automobile provides one switch that allows the user to select which of several external lights should be turned on, and other switches to select the mode of operation and fan speed of the heater/air conditioner.
Often the selector device is a rotary switch in which a movable contact is connected to a knob. When the user rotates the knob, the movable contact sequentially engages different stationary contacts, each of which is associated with a circuit for a different function to be selected. One of the drawbacks of such mechanical contact switches is that the contacts wear with usage and corrode with the passage of time. Therefore, it is desirable to provide a non-mechanical contact mechanism for selecting among the different functions.
Automobiles also provide switches that enable the driver to control motors which raise and lower the windows. A lever or rocker actuated switch typically is mounted on the inside surface of the door, by which the driver or passengers control a motor to position the window. Although the switch may directly control the application of electricity to the motor, often different positions of the switch merely provide an input signal to a motor control circuit. In one switch position, the control circuit energizes the motor to lower the window only while the user holds the switch in that position and the motor stops whenever the user releases the switch lever. When the user places the switch in an express-down position, the motor controller responds by activating the motor continuously until the window is in the fully lowered position, even if the user releases the switch lever before the window reaches the fully lowered position. The express down feature is particularly useful when using a drive-up window or toll booth in which case the window can be fully lowered with a single, quick motion of the control switch without having to hold the switch while the window slowly lowers. A similar set of control switch positions also are provided for manual and express raising of the window.